Power transmission



Sept. 7, 1943. I K. R. HERMAN ETA L 2,328,979

POWER TRANSMISSION Filed May 16, 1942 INVENTOR KENNETH R. HERMAN & y 1,-- IS T. HARRINGTON 3 7 ATTORNEY Patented Sept. 7, 194.3

- UNITED STATES PATENT OFFICE rowan TRANSMISSION Kenneth R. Herman, Franklin, and Ferris '1. Harrington, Detroit, Mich assignors to Vickers Incorporated, Detroit, Mich, a corporation of Michigan Application May 16, 1

942, Serial No. 443,218. x

6 Claims. (01. 121-45) This invention relates to power transmissions,

particularly to those or the type-comprising two or more fluid pressure energy translating devices, one of which may function as a pump and an-' other as afluid motor.

Transmissions of this character are widely used on machine tools for actuating reciprocating slides, rotary spindles, etc." It-is frequently necessary in applications of this character to make provision for sudden and wide fluctuations in motor load, as, for example, when a cutting tool breaks through. a work piece, and to so arrange the circuit that the motor is positively prevented from ever jumping ahead under a sudden relief in load.

There are in use several methods which accomplish this result, one method comprising the use of a back-pressure valve in the motor outlet In the drawing: I

Thesingle figure is adiagrammatie view of a power transmi'ssion system embodying a preferred form or the present invention.

There is indicated at III a pump adapted to be driven by a suitable prime mover, such as anelectric motor 12. The pump l0 withdraws fluid from a; tank l4 through a suction conduit 18 and delivers the same to a delivery conduit l8. The latterhas arelief valve 20 of conventional construction for bypassing oil to the tank l4 line which acts to maintain a predetermined back pressure therein. Systems of this character present one drawback particularly troublesome in large size machine s, namely, that the back-pressure valve is an energy dissipator, and, if the back pressure which must be maintained is very 1 high and the volume of fluid passed therethrough is also high. a considerable heating oi'the oil occurswhich adversely affects the system as a whole. In addition, the waste of power at the back-pressure valve requires a larger power input to the machine and thus gives 'th'ecircuit as a whole a low eiflciency.

It is an object of the present invention to provide an improved power transmission system a wherein the. above difliculties ar avoided, at least to asubstantial extent, and at the same time to positively prevent any jumping ahead of the fluid motor undera sudden relief in load.

A further object is to provide a system of this character wherein a relatively low value of back pressure is normally maintained in the motor 'is the pressure port, 30 and 32 the cylinder ports,

outlet when the motor load is sufficiently high to, of itself, prevent lumping ahead. At the same time, additional means are provided for increasing the back pressure to a higher value whenever motor load falls below a certain value.

In this way-a a assured that the high back pressure necessary to'previit tome ahead is an; plied only during'intervals when jumping ahead is otherwise likely to occur.

Further objects and advantages of the present invention will be apparent from the following description', reference being had; to theaccompanying drawing wherein a'preferred form of the present invention is clearly shown.

through a conduit 22 whenever a predetermined pressure is exceeded in the delivery conduit IS.

Th conduit I8 extends to a directional tourway valve 24 which directs the flow oi liquid irom'pump II) to and from. either end of the cylinder 54. The directional valve 24 comprises a main body member having a longitudinal bore 26 within which is mounted a slidable spool 45.

The bore 2-5'is provided with a plurality of annular ports arranged along its 1ength,'oi which 28 and 40' and 42 the tank ports. The pressure port communicates with the delivery conduit l8, while the tank ports 40 and 42 communicate withtank 14 through a conduit 44; The cylinder ports 30 and 32 communicate with motor conduits 36 and 38, respectively, which lead to the opposite ends, of a fluid motor 54. The latter comprises a cylinder within which is mounted a movable piston 58 rate of liquid flow thereto. Valve 60 includes an adjustable throttle valve '62 which limits the rate of fluid flow and a pressure compensator 64 which maintains the rate of controlled flow independent or the variations in the operating pressure or fluctuations in cutting tool resistance. The pressure compensator 64 consists of a piston 88, piston spring 68 and a valve Ill controlling the fl0W' 110l 11 port 18 into a chamber ll. Piston "is mounted in a cylinder" irom which two passages 14 and 16 extend, one from each-side of the piston 56. to the opposite sides ofthe throttle B2. A light spring 68 tends to keep Open valve 64 by urging it to the left. The hydrostatic pressure compensator i4 regulates the fluid flow to sage 9| of body 84..

the throttle 82 in accordance with'the pressure drop across the throttle 82, thatis, as pressure in chamber Il rises slightly, the piston 88 'will move to the right, pressure on its left side bein greater than that on its right, and continue to close valve I8 until the rate of liquid flowing into chamber II is the same as that of the liquid being discharged throughthe throttlel82'. Sinceth rate of discharge through the throttle 82 will remain constant, the rate of movement of the working tool willalso be relatively constant. 1 The flowcontrol valve 88 contains an integral:

delivered through conduit I8 .to the directional valve 24. With the spool 48 in neutral position, illustrated, the full pump delivery is bypassed to the tank I4 through a relief valve 28 via conduits 22 and 44,.

To advance the piston 58, lever 48 of valve 24 is pushed inward. This action allows the pump '10 fconduit '38 to the flow control valve 88; The liquid will enter chamber II through the opening check valve*82 to providefor the reverse ,flow..- Y

A drain conduit 88 connects the end of throttle valve 82, at a-point below the plane of the drawing, with'the'exhaust conduit for the purpose valve. p i I Attached to the exhaust end of the cylinder 54 by aconduit 38 are two bypass ,valves 84 and 98 connected in series for providing back pressure, therein to firmly hold the, piston '58 as it moves seepage along the stem of the throttle a 31 leading to the valve 88.

' The discharging liquid from the back of piston ldelivery to be-directed from the pressure port 28 to the. motor port 88 where it is delivered by formed by valve 'I8to thethrottle 82 where it is metered into the inlet line 38of cylinder 54 and forcesback'piston 58 at a certain rate-of speed asv determined by the adjustment of the throttle through its work strokef Valve 84 comprises a in bore 85. a

The body alinollldes Mounted on. the left end face of the body 84 is of cap 95 and in directcommunication with fpasn the righthand endof the main body is secured an end cap I through which is threaded an adjusting screw 98; 'A spring 94 extends from I within the screw 98 to the valve spool 88 holding I it in a closed position to the left, disconnecting ports I00 and IN. The spring 94 isadjusted by the screw 98 to whatever back pressure in cylinder 84 is desired. A chamber I II in the end cap I05 is in communication with the end of the bore 85 for exhausting oil therefrom as spool 88 recip-= rocatesin bore 85. Leading from-chamber III is a passage I I8 having anauxiliary branch passage H5 which extends to the end of cap I05 and in a communication withpassage 98 of body 84. The I end. cap I08 also carries a lock nut H8 and a closure cap I", both secured on the screw 98.

Port I8I, of valve communicates with port H8 of valve 98 through a conduit 38. 'Valve 98.

latter is nects with passage I29 which extends to the side of the end cap Iand is in communication with v inlet line 98 througha conduit 81. The setting of springt l88 is much higher'than that of spring 94 of valve 84. I

- To provide for rapid ,retuma check valve I48 ismounted onto conduit 38 which extends from the directionalvalve 24. has a conduit I42 extendingto the rod end of cylinder 54, circumventing valves 84 and 98.-

. In operation, whilethe pump I8 is being drivenby'the electric motor I2, 011 is withdrawn from.

a pair of auxiliary passages9l and 93 extending from ports I88 and I8 I, 1 respectively,to the end face of the body 84.

Thecheck valve I 48 v main body having a central longitudinal bore 85 1 which is provided with ports I08 and I8 I, communication between which is controlled by a movable spool 88. The latter has two lands 8I"and 89 which are freely slidable with a liquid tight fit valve, 82. The metered liquid also enters conduit 58 will,as it flows through valves 84 and to tank, be ,restrictedto build up a back pressure g on the discharge end of the cylinder 54 to prevent'surging of the piston 58 after the work is completed and also to maintain back pressure proportional to the load fluctuations, thus "we.

. venting jerkyaction on-the feed stroke.- v

Valve 84*rest'ricts the'fiow of the'discharged" liquid by causing-it to encounter a resistance at portfI88. beforeffiowing through it to 'port' I8I,'

and to'valve 98 via conduit 38. This resistance is overcome whenever pressure in port I88 rises f above the value forlwhich the spring 94 is set. Y'. 1

pressure is transmitted through passages '9I,'-9'9,iand 91 to the valve actuating chamber I I83v where it acts on; valve spool 88, opening" it and-permitting the liquid to pass to port I8l.

' Valve 98' will open to allow the dischargeliquid to -flow to tank when a'certain fluid pressure is;

admitted to the chamber I22 through passage I29 which communicates with the inlet1 conduitf38" through conduit 8|.-*This pressure controls the amount of liquid that will be bypassed to the tank changing with'load vari-.

I4 through port I3I, ations;

During the to overcome, before the piston 58 can be'forced back, pressure .in conduit 81 must -be built up to exceed the value of the setting or the spring I80 of valve 98.. Before the opening of valve 98, the discharge liquid will be admitted intoport I is because of the lower setting of valve 84.- At-this phase, valve 98 determines the back, pressure in cylinder 54.

*As the load on the rod 58 increases, pressure will also increase in-the inlet conduit 38 which willbe transmitted to chamber I22 causing the spool I 21 to be moved more to the right, allow ing the liquid to be discharged with less resist- .ance, thus lessening the back pressure. Thus,. whenfthe spool I21 is in the extreme right posi-,

tion, the back pressure will equal merely'the pressure needed to keep valve 84 open;

Upon the lessening of the load to apolnt below I the setting of valve 98, pressure in the inlet con-- duit 36 will also lessen and accordingly will lessen in chamber I22, This will tend to close the valve spool I 2101 valve 98, thus creating a greater back pressure in motor outlet line 38 which replaces,

so to speak, the load resistance which, was reduced.

To reverse the operation, returning the piston feeding o eration with 'a'ze ro load discharging from the front of piston 56 will be bypassed around flow control valve 60, through 5 conduit Bl, unseating check valve 82, to port 18 where it is delivered to valve 24 by conduit 36.

The valve spool 46, being in the extreme right position, will direct the liquid to the tank conduit 44 leading to the tank M.

It will be seen that th present invention maintains back pressure while ffeeding-in and at the same time keeps the oil in the circuit much coolerthan heretofore because during normal load conditions the motor exhaust fluid flow passes to the tank through a low-pressure, back-pressure valve.

While the form of embodiment of the invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

What is claimed is as follows: I

1. In a hydraulic power transmission system the combination with a source of pressure fluid,

a fluid motor operable by fluid supplied from said source, supply and return conduits connecting,

the source'with the motor, a flow controller in the supply line for regulating the rate of flow to the motor, a back pressure valve in the return conduit and responsive to motor outlet pressure for maintaining a predetermined low back pressure in the motor outlet, and a second back pressure valve also in the return line and having an operative connection to the supply conduit whereby the second back pressure valve is responsive to the sum of the pressures produced in the supply conduit by the back pressure and by the motor load and is effective to impose additional back pressure only when the motor load is below a predetermined minimum.

2. In a hydraulic power transmission system thecombination with a source of pressure fluid, a fluid motor operable by fluid supplied from said source, supply and return conduits connecting the source with the motor, a flow controller-in the supply line for regulating the rate of flow to 'the motor, a back pressure valve in the return conduit and responsive to motor outlet pressure for maintaining a predetermined low backpressure in the motor outlet, and a second back pressure valve also in the return line in series with the other valve and having, an operative connection to the supply conduit whereby the second back pressure valve is responsive to the sum of the pressures produced in the supply conduit by the back pressure and by the motor loadand is effective to impose additional back pressure only a when the motor load is below a predetermined minimum.

motor outlet pressure for maintaining a predetermined low back pressure in the motor outlet, and a second back pressure valve also in the return line and having an operative connection to the supply conduit whereby the second back pressure valve is responsive to the sum of the pressures produced in the supply conduit by the back pressure and by the motor load and is effective to impose additional back pressure only when the V I motor load is below a predetermined minimum.

4. In a hydraulic power transmission system the combination with a source of pressure fluid, a fluid motor operable by fluid supplied from said source, supply and return conduits connecting the source withthe motor, means for maintaining a predetermined minimum back pressure in the outlet from the motor under all conditions, and means for imposing additional back pressure only when the motor load falls below a predetermined minimum.

5. In a hydraulic power transmission system the combination with a source of pressure fluid, a fluid motor operable by fluid supplied from said source, supply and return conduits connecting the source with the motor, means for regulating the rate of flow to the motor, directional control means for selectively directing fluid to the motor in one direction or the other, a back pressure vvalve in the return conduitand responsive to motor outlet pressure for maintaining a predetermind low back pressure in the motor outlet, a second back pressure, valve also in the return line and having an operative connection to the supply conduit whereby the second'back pressure valve is responsive to the sum of the pressures produced in the supply conduit by the back pressure and by-the motor load and is effective to impose additional back pressure only when the motor load is'below a predetermined minimum, and a single check valve arranged to bypass both back pressure valves during flow to the motor in one direction.

6. In a hydraulic power transmission system the combination with a source of pressure fluid. a fluid motor operable by fluid supplied from said source, supply and return conduits connecting the source with the motor, a flow controller in the supply line for regulating the rate of flow to the motor, and including a throttl and a compensating valve responsive to the pressure drop through the throttle for maintaining such pres- .sure drop substantially constant, a back pressure valve in the return conduit and responsiveto motor outlet pressure for maintaining a predetermined low back pressure in the motor outlet, and a second back pressure valve also in the return line and having an operative connection to the supply conduit whereby the second back pressure valve is responsive to the sum of the pressures produced in the supply conduit by the back pressure and by the motor load and is effective to impose additional back pressure only when the motor load is below a predetermined minimum. 

